1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for an alternative cooling system for the suppression pool of a Boiling Water Reactor (BWR) nuclear reactor. The cooling system may be particularly beneficial in the event a plant emergency that causes plant electrical power to be disrupted, or normal cooling of the suppression pool to otherwise become impaired. The cooling system may also be used by the suppression pool to supplement the conventional residual heat removal system.
2. Related Art
FIG. 1 is a cut-away view of a conventional boiling water nuclear reactor (BWR) reactor building 5. The suppression pool 2 is a torus shaped pool that is part of the reactor building primary containment. Specifically, the suppression pool 2 is an extension of the steel primary containment vessel 3, which is located within the shell 4 of the reactor building 5. The suppression pool 2 is positioned below the reactor 1 and spent fuel pool 10, and is used to limit containment pressure increases during certain accidents. In particular, the suppression pool 2 is used to cool and condense steam released during plant accidents. For instance, many plant safety/relief valves are designed to discharge steam into the suppression pool 2, to condense the steam and mitigate undesired pressure increases. Conventionally, a BWR suppression pool 2 is approximately 140 feet in total diameter (i.e., plot plan diameter), with a 30 foot diameter torus shaped shell. During normal operation, the suppression pool 2 usually has suppression pool water in the pool at a depth of about 15 feet (with approximately 1,000,000 gallons of suppression pool water in the suppression pool 2, during normal operation).
The pool 2 is conventionally cleaned and cooled by the residual heat removal (RHR) system of the BWR plant. During normal (non-accident) plant conditions, the RHR system can remove water from the suppression pool 2 (using conventional RHR pumps) and send the water through a demineralizer (not shown) to remove impurities and some radioactive isotopes that may be contained in the water. During a plant accident, the RHR system is also designed to remove some of the suppression pool water from the suppression pool 2 and send the water to a heat exchanger (within the RHR system) for cooling.
During a serious plant accident, normal plant electrical power may be disrupted. In particular, the plant may be without normal electrical power to run the conventional RHR system and pumps. If electrical power is disrupted for a lengthy period of time, water in the suppression pool may eventually boil and impair the ability of the suppression pool to condense plant steam and reduce containment pressure.
In a plant emergency, use of the RHR system may cause highly radioactive water (above acceptable design limits) to be transferred between the suppression pool and RHR systems (located outside of primary containment). The transfer of the highly radioactive water between the suppression pool and RHR system may, in and of itself, cause a potential escalation in leakage of harmful radioactive isotopes that may escape the suppression pool. Additionally, radiation dosage rates in areas of the RHR system could be excessively high during an accident, making it difficult for plant personnel to access and control the system.